Field of the Invention
The present invention relates to a display device, and more particularly, to a display device that may minimize voltage drop of a power source supplied to a pixel.
Discussion of the Related Art
Recently, with the development of multimedia, importance of flat panel display devices has been increased. In response to this trend, flat panel display devices such as liquid crystal display devices, plasma display devices and organic light emitting display devices have been commercialized. Of the flat panel display devices, the organic light emitting display device has received much attention as a flat panel display device for next generation owning to advantages of fast response speed, low power consumption, and excellent viewing angle characteristic based on self-light emission.
A related art organic light emitting display device includes a display panel, which includes a plurality of pixels formed in a pixel region defined by crossing between a plurality of data lines and a plurality of gate lines, and a panel driver emitting light from each pixel.
Each pixel of the display panel, as shown in FIG. 1, includes an organic light emitting device OLED and a pixel circuit PC.
The pixel circuit PC includes a switching transistor Tsw, a driving transistor Tdr, and a capacitor Cst.
The switching transistor Tsw is switched in accordance with a scan pulse SP supplied to a scan control line SL, and supplies a data voltage Vdata, which is supplied to a data line DL, to the driving transistor Tdr.
The driving transistor Tdr is switched in accordance with the data voltage Vdata supplied from the switching transistor Tsw and controls a data current Ioled flowing to the organic light emitting device OLED by using a driving power source VDD.
The capacitor Cst is connected between gate and source terminals of the driving transistor Tdr, and stores a voltage corresponding to the data voltage Vdata supplied to the gate terminal of the driving transistor Tdr and turns on the driving transistor Tdr at the stored voltage.
The organic light emitting device OLED is electrically connected between a source terminal of the driving transistor Tdr and a common voltage line Vss and emits light through the data current Ioled supplied from the driving transistor Tdr.
Each pixel P of the aforementioned related art organic light emitting display device controls a size of the data current Ioled flowing in the organic light emitting device OLED by using switching of the driving transistor Tdr based on the data voltage Vdata, thereby displaying a predetermined image.
In the aforementioned related art organic light emitting display device, light-emission luminance of each pixel is affected even by the driving power source VDD together with the data voltage Vdata. Accordingly, a uniform voltage of the driving power source VDD should be supplied to each pixel to obtain uniform luminance of each pixel.
However, the driving power source VDD is a current power source having a set voltage level, and according to the related art organic light emitting display device, voltage (IR) drop occurs in the driving power source VDD supplied to each pixel due to line resistance of a driving power line PL. The voltage drop of the driving power source VDD is more increased if the organic light emitting display device has a large area.
FIG. 2 is a diagram illustrating a crosstalk test pattern displayed on a display panel in a related art organic light emitting display device.
If a crosstalk test pattern having a rectangular white pattern on a gray background is displayed as shown in (a) of FIG. 2, in the related art organic light emitting display device, bright line/dark lines A occur in a boundary of the crosstalk test pattern due to voltage drop of the driving power source VDD, whereby vertical crosstalk occurs. The bright line/dark lines A are increased if a size of the crosstalk test pattern is increased.
FIG. 3 is a graph illustrating a current ratio according to a size of a rectangular white pattern in a crosstalk test pattern in a related art organic light emitting display device. In FIG. 3, B is a graph illustrating an ideal current ratio, and C is a graph illustrating a current ratio according to a size of a rectangular white pattern.
If the size of the rectangular white pattern is increased by voltage drop of the driving power source VDD, the current ratio is reduced.
Accordingly, there is a need for a method for reducing the voltage drop of a power source supplied to a pixel.